This invention relates to the creation of Bragg reflective gratings in photosensitive optical waveguide, and in particular to the creation of such gratings in forms exhibiting chirp or apodisation.
A method of providing such shading, chirp or apodisation is described by H. N. Rourke et al in a paper entitled `Fabrication and Characterisation of Long, Narrow-Band Fibre Gratings by Phase Mask Scanning`, Electronics Letters (4 Aug. 1994) Vol. 30, No. 16 pp 1341-2. In that instance the Bragg grating is created in an optical fibre by lateral exposure of the fibre to ultra-violet light through a phase grating mask. The ultra violet light is scanned across the mask in the axial direction of the fibre, and it is explained that, by appropriate programming of the speed of the scan, the exposure time can be tailored to a particular function of position along the length of the developed Bragg grating.